In mobile data processing devices, for example portable and mobile telephones and computers, conservation of battery power is very important. Whenever the data processing circuitry within the device is not being used, it can often be disabled from operation, thereby permitting power savings. However, even with circuitry disabled, there can often remain the problem of leakage currents at the inputs of an integrated circuit device that contains the data processing circuitry. The greater the input leakage current while disabled, the greater the battery power consumption at a time when the device is not even being utilized. Moreover, in some mobile data processing devices, a given integrated circuit might actually be disabled for a large majority of the time that the device is in operation.
For example, some mobile data processing devices support wireless communications. Some wireless communication standards, for example GSM, support a wireless communication protocol known generally as time division multiple access (TDMA). In TDMA applications, the mobile data processing device actively communicates over the wireless communication interface only during predetermined portions of the time that the device is in operation. For example, in GSM, a given mobile device actively communicates via the wireless communication device only during one-eighth of its operating time. During the remaining seven-eighths of the time, a given device is inactive while other devices are using the wireless communication link. Accordingly, a TDMA device can realize significant savings in battery power by simply disabling all circuitry which supports wireless communications during the time that the device is not actively engaged in wireless communication.
FIG. 1 illustrates an example of a mobile device which utilizes a wireless communication interface. In the example of FIG. 1, a CMOS controller IC 12 is powered by a battery 11. The CMOS controller IC 12 controls a power amplifier (PA) 13 which amplifies an input RF signal to produce an output RF signal. An antenna apparatus 14 transmits the RF output signal across a wireless communication interface 15. The CMOS controller IC 12 includes a digital transmit enable input terminal (or input pin) 16, designated TX ENABLE. This transmit enable input is used to enable the CMOS controller IC 12 during the period of time (for example one-eighth of the time) in which the device is actively communicating via the wireless link 15, and to disable the CMOS controller IC 12 during the period of time (for example seven-eighths of the time) in which the device is not actively communicating via the wireless link 15. As shown in FIG. 1, the CMOS controller IC 12 includes other digital input terminals (or pins) designated generally at 17. The digital input terminals illustrated at 16 and 17 receive input signals provided by a baseband processor IC in the mobile device.
If the baseband processor IC has been produced using deep submicron technology, then the input signal levels provided to the CMOS controller IC 12 at 16 and 17 can be as low as 1.2–1.7 volts. The battery 11 typically provides a power voltage in the range of 2.7–5.5 volts. The input pins at 16 and 17 typically drive into circuit structures such as inverters. However, a 1.2–1.7 volt input signal cannot be expected to cleanly switch an inverter circuit which operates from a 2.7–5.5 volt power supply. This means that the input inverters can be expected to exhibit leakage current, regardless of whether the transmit enable pin 16 is activated to enable the CMOS controller IC 12, or is inactivated to disable the CMOS controller IC 12. The current drawn by the controller 12 when inactivated is often referred to as standby current.
One conventional approach to the mismatch between the 1.2–1.7 volt input range and the 2.7–5.5 volt battery range is the use of a regulator to lower the effective supply voltage seen at the input inverters to a level around 1.5 volts. This can permit full on/off states to be achieved without leakage, but the regulator requires a relatively large amount of circuit area, and must also be on at all times, even when the transmit enable pin is deactivated. Thus, much or all of the leakage current that is saved by operation of the regulator must still be drawn to power operation of the regulator anyway.
Moreover, the digital inputs at 17 in FIG. 1 are typically non-deterministic in nature, which means that the digital high/low switching of the signals is not known during the period of time while the transmit enable signal is deactivated. Accordingly, the switching action of these pins while the controller 12 is disabled causes leakage currents during the switching, and these leakage currents are not addressed by the regulator approach described above.
Therefore, there is a need in the art to provide for reduction of leakage currents at IC inputs that receive very low voltage signals, without adversely impacting the overall supply current budget. There is also a need to reduce leakage currents due to non-deterministic input switching that occurs while the IC is disabled.